An unmanned drone has crashed on a South Korean island close to the disputed maritime border with the communist North.

The unidentified aircraft fell on Baeknyeong island on the same day as artillery fire was exchanged in the area between forces from the North and South.

The South Korean military are reported to be examining any possible link to spying operations by Pyongyang.

An official is reported as saying the drone is up to 10 feet long, with a Japanese engine and Chinese parts, along with a small camera.

Image Caption:North Korean "drones" on show at a military parade last year

The drone is similar to another found in a border city last month.

North Korea released footage last year of practice drones modified to crash into set targets, but is not thought to have unmanned craft capable of carrying out air strikes or long-range surveillance flights.

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The discovery is likely to further heighten tensions in the area after Pyongyang carried out live firing drills that saw more than 100 shells fall in South Korean waters.

Seoul responded to what it branded "premeditated provocation", with its own artillery and scrambled fighter jets.

The US also condemned North Korea's actions as "dangerous and provocative".

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Anxious residents sought refuge in shelters on Yeonpyeong island, where North Korean artillery killed four South Koreans in 2010.

The de facto maritime border between the two countries - the Northern Limit Line - is not recognised by Pyongyang.

The artillery exchange came a day after North Korea warned it had not ruled out a fourth test of its nuclear deterrent in retaliation for the US conducting "madcap nuclear war" exercises in South Korea this month.

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Every year the US and South Korea conduct joint battle exercises involving around 12,500 US and as many as 200,000 South Korean troops.

The annual drills are regularly condemned by the North as preludes to a US invasion, though Washington insists the exercises are defensive.

China called for calm, while Russia said it was "worried" by Pyongyang's declaration it may conduct a further nuclear test.